1. Field of the Disclosure
Embodiments disclosed herein relate generally to a process for the reduction or removal of benzene in a gasoline fraction. More specifically, embodiments disclosed herein relate to the removal of benzene from a reformate stream. Removal of benzene may be accomplished via the alkylation of benzene with an alcohol or an ether via catalytic distillation.
2. Background
The demand for cleaner and safer transportation fuels is becoming greater every year. Two major sources of gasoline feedstock, including reforming and catalytic cracking, present both a problem meeting strict environmental regulations and impose certain health risks. For example, light reformate typically contains unacceptably high levels of benzene, a known carcinogen.
Refiners in the U.S. and in other countries are required to remove benzene from reformate streams and other gasoline fractions. Various options for the removal of benzene from such streams may include distillation, extraction, hydrogenation, alkylation, and transalkylation. However, due to the low concentrations of benzene in these streams or a limited quantity of benzene contained in reformate and other streams, it may be uneconomical for a non-integrated refiner to recover benzene from various gasoline fractions, such as reformate, for example. In addition, the refiner may not have access to a market into which he might sell the benzene.
Extraction of benzene requires expensive capital investment in necessary equipment and a customer for the benzene product, neither of which may be feasible for a small, non-integrated refiner. Also, while it is possible to extract benzene from the gasoline pool by fractionation techniques, such techniques are not preferred, because the boiling point of benzene is too close to that of some of the more desirable organic components, including C6 paraffins and isoparaffins. Monoalkylate aromatics (monoalkylate), such as toluene, xylenes, and ethylbenzene are more desirable for gasoline blending, as opposed to benzene, because they are less objectionable both from an environmental and a safety point of view. Additionally, toluene, xylenes, and ethylbenzene each have a higher octane rating than benzene.
Alternatively, benzene in reformate may be removed via hydrogenation. However, hydrogenation of aromatics, such as benzene, results in reduced octane rating and thus diminishes the overall value of the fuel. As with extraction, hydrogenation of benzene also may not be feasible for a small refiner due to the potentially uneconomical costs of supplying hydrogen.
Alkylation of benzene with an olefin to form a monoalkylate product is another option available to refiners. Various processes for the alkylation of benzene are described in, for example, U.S. Pat. Nos. 4,371,714, 4,469,908, 5,118,897, 5,080,871, 5,118,872, 4,891,458, 4,008,290, 5,003,119, 5,902,917, 5,998,684, 5,087,784, 7,038,100, and 7,297,829, among others.
Alkylation processes, such as those mentioned above, in general, may not be as effective in upgrading the overall fuel value of reformate, largely due to the production of polyalkylate by-products. Also, alkylation may require a readily available olefin source, and therefore may not be feasible for small refiners.
Accordingly, there is still a significant need in the art for economical methods to reduce the levels of benzene in refinery streams, especially for smaller, non-integrated refining operations.